Platinum Binds Proteins in the Endoplasmic Reticulum of S. cerevisiae and Induces Endoplasmic Reticulum Stress

Pt­(II)-based anticancer drugs are widely used in the treatment of a variety of cancers, but their clinical efficacy is hindered by undesirable side effects and resistance. While much research has focused on Pt­(II) drug interactions with DNA, there is increasing interest in proteins as alternative targets and contributors to cytotoxic and resistance mechanisms. Here, we describe a chemical proteomic method for isolation and identification of cellular protein targets of platinum compounds using Pt­(II) reagents that have been modified for participation in the 1,3 dipolar cycloaddition “click” reaction. Using this method to visualize and enrich for targets, we identified 152 proteins in Pt­(II)-treated Saccharomyces cerevisiae. Of interest was the identification of multiple proteins involved in the endoplasmic reticulum (ER) stress response, which has been proposed to be an important cytoplasmic mediator of apoptosis in response to cisplatin treatment. Consistent with possible direct targeting of this pathway, the ER stress response was confirmed to be induced in Pt­(II)-treated yeast along with in vitro Pt­(II)-inhibition of one of the identified proteins, protein disulfide isomerase.